1. Field of the Invention
This invention relates to a hotmelt adhesive composition containing a polyamide based on dimeric fatty acids and, optionally, a second polyamide and/or polyethylene.
2. Description of Related Art
Hotmelt adhesives are becoming increasingly important in the adhesives field. These adhesives are advantageous since they reach necessary bond strength by cooling from the melt and, as such, are suitable for high-speed production operations. A further advantage resides in the fact that equipment for protection against solvent vapors is unnecessary. Moreover, the prolonged drying times of aqueous adhesives are substantially shortened when hotmelts are used.
An important class of hotmelts are the polyamides. Of these, polyamides based on dimerized fatty acids have acquired particular significance. Among the polyamides based on dimerized fatty acids, those containing dimerized fatty acids in the acid component and ether diamines in the amine component are particularly important as a result of their favorable low-temperature properties.
Thus, for example, German Application no. 27 54 233 describes copolyamide resins which contain in the acid portion of the molecule a special mixture of polymeric fatty acids (dimer fatty acids) and aliphatic dicarboxylic acids containing from 6 to 12 carbon atoms and, on the base side, a mixture of saturated aliphatic diamines and polyoxyalkylene diamines. These products have an embrittlement temperature of -25.degree. C.
Similar resins are described in U.S. Pat. No. 4,218,351 which relates to polyamides containing, in addition to the usual raw materials, from 5 to 30 mole percent dimer fatty acid and from 0.25 to 12.5 mole percent oligomers containing amino groups (polyoxyalkylene diamines).
A polyamide mixture is described in German Patent Application no. 31 11 206, according to which a polyamide based on dimerized fatty acids and polyether diamines is mixed with a second polyamide based on dimerized fatty acids and aliphatic amines or cycloaliphatic amines containing from 2 to 40 carbon atoms in the carbon chain, free from hetero atoms.
Although products of the above type show a favorable spectrum of properties, it is still desirable to improve the substrate adhesion, particularly to difficult substrates. The need exists to improve the peel strength of bonded assemblies obtained with hotmelt mixtures such as these, while, at the same time, retaining their favorable low-temperature properties.